Sediment-borne “seeds” from Sand Creek, northwestern Kansas: taphonomic significance and paleoecological and paleoenvironmental implications

Abstract

A study of seeds, fruits, and reproductive bracts (collectively “seeds”) collected during 1986–1988 from recent sediments along a small, perennial stream in northwestern Kansas was conducted to determine the taphonomic significance of sediment-borne “seeds” and the implications for studies of similar accumulations of fossil plants. The samples were collected from sediments in, but at the margin, of a flowing stream. The abundant and diverse assemblage of aquatic and marginal-aquatic plants recovered in the sediments shows that the sediment-borne “seeds” accurately reflect the marginal-aquatic habitat next to the channel and temperate climate of the region. The sediments also contained a wide assortment of other taxa that represented native riparian, floodplain, and upland habitats, as well as cultivated croplands; overall these taxa are indicative of temperate grasslands. Disturbance of the study site by trampling by livestock, and perphaps by lowered stream flow during the last year, reduced the variety of taxa and numbers of specimens in samples, but these influences did not change the marginal-aquatic habitat suggested by sediment-borne “seeds”. Comparison of a late Miocene (7–8 m.y. B.P.) assemblage of “seeds” from the Minium Quarry in northwestern Kansas with the Sand Creek results suggests that the habitat nearest the deposition site of the fossils was a marginal-aquatic setting similar to that Sand Creek. The comparison alos suggests that the Miocene landscape beyond the depositional site was dominated by warm temperate to subtropical grasslands, an interpretation supported by faunal evidence.